This description relates to fabricating semiconductors.
Patterns may be fabricated on a semiconductor (e.g., a silicon wafer) by transmitting beams of light through a mask and onto a surface of the semiconductor. In order to produce patterns with extremely small pitches (i.e., the distances between lines) on a semiconductor a phase shifting mask (PSM) may be used. PSMs cause the shifting of the phase of a light source so that the peaks of one wave of light lines up with the valleys of an adjacent wave, effectively canceling each other out and producing a dual-beam image (a “shadow” image) between the waves that is smaller than the two waves themselves. The dual-beam image may be used to fabricate patterns having pitches as low as one-half the theoretical minimum pitch of the light source. In the PSM fabrication technique, light source beams are transmitted through zero degrees and 180 degrees and, when passing through the PSM mask, result in cancellation of the zero degree order of the light.
Fabrication of semiconductor patterns may be achieved by performing a double-light exposure which refers to a first light exposure in a lateral axis (e.g., an “x-axis exposure”) followed by a second light exposure in a second orthogonal axis (e.g., a “y-axis exposure”).
“Negative” photoresistive materials (“resists”) may be used as part of a semiconductor patterning process. Negative resists refers to the property of a resist that becomes insoluble when exposed to a light beam, therefore the exposed area of the negative resists remains on the substrate after processing of the semiconductor substrate.